Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system subjected to partial loadings at different outdoor air temperatures

Abstract

This paper shows the performance evaluation of the variable refrigerant flow (VRF) air-conditioning system at different outdoor air temperatures during cooling and heating operations. The purpose of this study is to determine the real performance of the system when operating at different outdoor temperatures. The one outdoor unit's and two indoor units' VRF system was used as a test specimen in the controlled testing chambers in which temperature and humidity were controlled. Several test cases were done covering from partial to full thermal loadings for the different outdoor air temperatures. The results showed that the outdoor air temperature much affected the performance of the VRF air-conditioning system. It showed that during the cooling operation, as the outdoor air dry bulb temperature increases, the coefficient of the performance ratio decreases. In the heating operation, as the outdoor air dry bulb with corresponding wet bulb temperature decreases, the coefficient of the performance ratio decreases. The defrosting mode, which occurs during the heating operation, affects the indoor chamber's temperature as the air temperature becomes very low due to the indoor units having become an evaporator. The results of the study showed the importance of the VRF air-conditioning system performances at different outdoor air dry bulb and wet bulb temperatures. Hence, it is important to consider the outdoor air temperatures when calculating the energy consumption of the VRF air-conditioning system to be installed in new and/or retrofitted buildings as they affect the electric energy consumption.

Performance evaluation of the variable refrigerant flow (VRF) air-conditioning system during the heating-defrosting cyclic operation

“…The results also show the importance to be considered when the system operates at a low outdoor air temperature since the heating-defrosting cyclic operation results in changes of the indoor environment temperature. The results of this and previous studies regarding the real performance of the VRF air-conditioning system and its impact on energy consumption and indoor environmental conditions at different conditions which happen during real operation is important to be considered both in energy consumption of buildings and in the maintenance of buildings required indoor thermal environment (Enteria et al, 2016a;Enteria et al, 2016b Greek letter α Load balance ratio (α = 1, Balanced; α < 1, Unbalanced)…”

“…Only balanced loading is covered in this study which the heating-defrosting cyclic operation occurred. An unbalanced loading during the heating mode is presented in our previous study (Enteria et al, 2016b). Figure 4 shows the representative heating-defrosting cyclic operation of the VRF air-conditioning system.…”

“…The load balance ratio (α) is shown in Eq. (1) (Enteria et al, 2016b). In this measurement evaluation, α is equal to 1, the indoor chamber 1 load is equal to the indoor chamber 2 load.…”

“…As the VRF air-conditioning system is expected to encounter heating mode operation in locations with a winter season, the performance evaluation of the system in this climatic condition is important. The review of the previous studies shows that the evaluation of the VRF air-conditioning system occurring during the heating-defrosting cyclic operation has not yet been done in detail (Enteria et al, 2016a;Enteria et al, 2016b;Horie and Hihara, 2012;Watanabe et al, 2009;Watanabe et al, 2007). This paper shows the evaluation of the VRF air-conditioning system with one outdoor unit and two indoor units operated under different very low outdoor dry bulb temperatures and different wet bulb temperatures in which ice accumulation occurred in the outdoor unit heat exchanger.…”